The present invention relates to a method and a system for tuning a resonance module in a radio base station. The resonance module having tuning means, a transmitter connection, and an antenna connection. High-frequency input and output signals on the transmitter and antenna connection, respectively, are sensed and processed to tune the resonance module to a frequency of the input signal on the transmitter connection. The processing of the sensed input and output signals includes processing in a low-frequency range.
Such an arrangement for tuning resonance modules is disclosed in the published PCT Application No. SE92/0004. That resonance module includes a resonant cavity and a resonance body, the position of which is adjustable by means of a motor to control the resonance frequency of the resonance module. As long as there is a phase difference between high-frequency input and output signals of the resonance module, the arrangement adjusts the position of the resonance body so as to reduce that phase difference. This prior art arrangement includes a voltage controlled oscillator that generates a high-frequency signal which is mixed with the input signal and the output signal in first and second mixers, respectively. Thus, two low-frequency signals are formed, the phase difference of which is a measure of a mistuning of the resonance module. Dependent thereon, the resonance module is tuned by means of the motor to a correct resonance frequency being the frequency of the input signal of the resonance module.
However, in this prior art arrangement, the voltage controlled oscillator is a relatively complicated and expensive component, which is required to have high dynamic performance since a relatively wide frequency range has to be scanned in the prior art tuning method.